1. Technology Field
The present invention generally relates to semiconductor optical devices. In particular, the present invention relates to a method for etching facets of a laser prior to coating in such a way as to control the formation of substances that can undesirably produce leakage current during laser operation.
2. The Related Technology
Semiconductor lasers are currently used in a variety of technologies and applications, including communications networks. One type of semiconductor laser is the distributed feedback (“DFB”) laser. The DFB laser produces a stream of coherent, monochromatic light by stimulating photon emission from a solid state material. DFB lasers are commonly used in optical transmitters, which are responsible for modulating electrical signals into optical signals for transmission via an optical communication network.
Generally, a DFB laser includes a positively or negatively doped bottom layer or substrate, and a top layer that is oppositely doped with respect to the bottom layer. An active region, bounded by confinement regions, is included at the junction of the two layers. These structures together form the laser body. A grating is included in either the top or bottom layer to assist in producing a coherent light beam in the active region. The coherent stream of light that is produced in the active region can be emitted through either longitudinal end, or facet, of the laser body. DFB lasers are typically known as single mode devices as they produce light signals at one of several distinct wavelengths, such as 1,310 nm or 1,550 nm. Such light signals are appropriate for use in transmitting information over great distances via an optical communications network.
The two facets of the DFB laser described above are typically coated with a coating material that optimizes the emission of light from the active region. However, during formation of the various laser layers as detailed above, certain oxides, such as aluminum oxide, indium oxide and gallium oxide, can form on the facet surface. As such, prior to coating, the facets are often subjected to an argon physical etch process to remove any oxides that have formed on the facet surfaces.
Unfortunately after the argon etch—and though the identified oxides have been removed—metallic films, such as indium, gallium, or aluminum, can remain on the facet surface, having failed to be acceptably removed by the etching process. If left in place on the facet surface and coated over, these metallic films can represent a significant source of leakage current, also referred to herein as reverse leakage, for the laser during operation. Such reverse leakage compromises the reliability of the laser and can even lead to electro-static discharge (“ESD”) damage in some cases.
Therefore, a need exists in the art for a method of removing metallic films from the facet surfaces of a laser, such as a distributed feedback, Fabry-Perot, or other laser, prior to facet coating so as to improve device reliability and performance.